The present invention relates to a screw compressor comprising a casing, a male and a female rotor formed with axially twisted screw grooves arranged in the casing, the both rotors being rotated by timing gears fixed to the respective rotors while a desired minute gap is kept therebetween, and a method of manufacturing rotors therefor, and more particularly, to a screw compressor, in which leakage of a compressed air during rotation of the both rotors is less and a high compression efficiency is obtained, and a method of manufacturing rotors therefor.
With screw compressors, bores are formed in a casing to receive therein a male rotor and a female rotor. The bores include a male rotor side bore and a female rotor side bore, which are circular in cross section and parallel to each other. Respective axial centers of the male rotor side bore and the female rotor side bore are coincident with axes of the male rotor and the female rotor. The male rotor and the female rotor are rotated through timing gears with a minute gap between respective teeth of the male rotor and the female rotor, which gap eliminates short of contact between respective teeth, and rotation of the rotors causes suction and discharge of an air to be made use of for compressors and vacuum pumps.
An important problem in screw compressors resides in that a desired compression efficiency cannot be obtained since a compressed air leaks through a gap between a male rotor and a female rotor and a gap between the male and female rotors and bores receiving the rotors when the male and female rotors are rotated.
In order to solve the problem, hitherto, tooth profiles of respective rotors are formed with high accuracy, and there have been proposed as a working method therefor milling with formed tooth profile blades, hobbing with hob cutter, turning process with high-rigidity NC lathes, or the like (see JP-A-8-197331).
In the case where machining with high accuracy is demanded to obtain a high compression efficiency, the above conventional technique is not sufficient and a tooth profile is formed by means of grinding with a grinding machine provided with grindstone.
Since rotors are made of a material of high rigidity, grindstone abrades soon, or trial grinding with a new grindstone is necessary for maintenance of accuracy in the case where grindstone is replaced by a new one to perform grinding on rotors of a screw compressor having a different capacity, and while measuring a tooth profile, finish grinding is performed. Accordingly, there is caused a problem that hands and time are needed in the case of multi-product production.
Also, since grindstone used in grinding of rotors for screw compressors of a large capacity is large-sized and significantly heavy, a crane must be used at the time of grindstone replacement, which requires a manual work to present an obstacle to automatic working.